Improve generation of stubs to allow to generate them in parallel

[activeeon-bot]

Original issue created by Bastien Sauvan on 18, Aug 2014 at 15:11 PM - PALIGHT-66

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Currently, stubs cannot be generated in parallel in the same JVM because the class JavassistByteCodeStubBuilder is not thread safe. If several stubs are generated in parallel the static fields proxyGetter and proxySetter can be modified concurrently and thus makes the generation fails.
To solve this issue, there is at least 2 solutions:

• make the method createStubObjectMethods synchronized.
• the fileds proxyGetter and proxySetter are static fields only to be used in the method checkMethod where their signatures are used to ensure that there is no conflict with the methods to be reified. Thus, instead of storing the CtMethods proxyGetter and proxySetter, only their signature could be stored.